The following areas which bear on pituitary-gonadal interrelationships will be investigated: 1) Systematic studies of FSH production metabolic clearance rates in males with normal and abnormal gonadal function. 2) Determination of the minimal effective dose of HLH that will induce optimal testosterone levels in hypogonadotrophic eunuchoid males. 3) Establish whether FSH is synergistic with LH in stimulating Leydig cell function. 4) Further study of preliminary results which suggest that an altered feedback mechanism exists in patients with Klinefelter's syndrome. 5) Examination of the testicular ultrastructural characteristics of patients with oligospermia and correlation of findings with serum FSH titers. 6) Study the effects of LH releasing hormone in normal males and in hypogonadotrophic eunuchoidism. 7) Study the effects of aging on Leydig cell function.